An aneurysm is a localized dilation of a blood vessel wall which, if untreated, can rupture causing internal haemorrhaging, resulting in disability or death. Aneurysms are caused by degradation of the vessel wall due to atherosclerosis or infection. Cerebral aneurysms cause 32,000 deaths each year in the USA. In the case of cerebral aneurysms, haemorrhaging often triggers vasospasm. Vasospasm is a spasmodic contraction of the vessel wall, which results in constriction of blood flow to the brain. Vasospasm occurs in 50% of patients and accounts for 25% of severe disability and death.
Industries, in recent years, have looked to improve the current platinum endovascular embolization devices by coating them with hydrogels, aimed at improving the percentage fill of the aneurysm and reducing incidences of postoperative re-canalisation (reopening of the aneurysm to blood flow). In addition to this, surgeons have begun looking towards glues and embolization agents for the treatment of aneurysms, both for wide-neck aneurysms which cannot be filled using coils, and for more common aneurysm geometries due to their ability to more completely fill the aneurysm without leaving spaces which can become pressurised, resulting in re-canalisation. However, currently embolization agents are less than ideal and incidences of post-surgical complications, severe disability and death remain high.
A number of issues have been highlighted in the current methods for treatment of cerebral aneurysms. One of the major issues in the treatment of aneurysms occur in wide-neck aneurysms, wherein the fundus-to neck ratio <2.0. In these cases occlusion of the aneurysm becomes extremely difficult and risky, as embolization coils do not stay in place but migrate into the parent vessel, causing blockage. A similar situation arises whereby the proximity of a neighbouring artery causes a wide-neck-type aneurysm morphology and again can be difficult to treat using embolization coils and blockage of a parent or neighbouring artery can occur. A number of techniques have been attempted to resolve this issue but all require significant technical skill and carry a significant risk. As a result of these issues, many aneurysms go untreated.
A second issue which has been highlighted is irregular shaped aneurysms. Approximately only 1 in 9 aneurysms with complex shapes can be successfully treated using coil embolization. Location of the aneurysm is also an issue which affects the long-term outcome of the aneurysm treatment. Aneurysms which are in the direct path of blood flow have a much higher recanalization rate. In these cases, coils placed into the aneurysm tend to compress with time, providing little long-term protection from re-bleeds. Due to combinations of these issues, in approximately 34% of all cerebral aneurysms treated embolization remains incomplete.
In the majority of cases outlined above, a “wait and watch” approach is adopted, wherein the patient is subject to regular magnetic resonance (MR) or computer tomography (CT) imaging to examine the growth of the aneurysm. A conservative approach may also be followed, wherein the patient's lifestyle is modified and blood pressure is kept low by pharmacological means. However, both of these approaches place the patient in considerable risk of undergoing a cerebral haemorrhage. If the aneurysm is particularly large (>7 mm) and there is a high chance of a haemorrhage then an open craniotomy will be carried out, followed by surgical clipping. However, this procedure is only possible when the location of the aneurysm allows and subjects the patient to a higher risk of morbidity or mortality. New techniques have begun to become available to the clinician for treatment of wide-neck aneurysms, including 3-dimensional coils, dual microcatheter techniques, temporary inflation of a balloon to allow coil placement and intracranial stent placement. However, these techniques often fail to successfully embolize the aneurysm, they are highly skilled procedures carried out by few clinicians and they may increase the risk of vascular injury and thromboembolism. These treatments remain far from ideal for the clinician.
There therefore continues to be a need for improvements in treatment of aneurysms.